The present invention relates to a rotary compressor. More particularly, it relates to a rotary compressor of a type when an injection opening is formed in a bearing plate for a crank shaft for driving a rolling piston to supply a refrigerant into a compression chamber.
FIGS. 1 and 2 are cross-sectional views showing an important part of a conventional rotary compressor as shown in Japanese Unexamined Patent Publication No. 24260/1964. As shown in FIGS. 1 and 2, the conventional rotary compressor is so constructed that a crank shaft 3 having an eccentric part 2 is driven in a cylinder 1 by a motor so that a rolling piston 4 fitted to the eccentric part 2 is subjected to eccentric rotation in the cylinder 1 to thereby compress a refrigerant gas sucked in the cylinder 1. The crank shaft 3 is passed through and rotatably supported by both outer bearing plates 5, 6. A compression chamber A is formed between the both outer bearing plates 5, 6, inside the cylinder 1 and a vane 7 which is slidably held by the cylinder 1 and has an end portion being in contact with the outer circumferential surface of the rolling piston 4. An injection opening 8 for supplying the refrigerant into the compression chamber A is formed in either bearing plate, e.g. the bearing plate 6. The injection opening 8 is communicated with an exterior refrigerant circulating circuit through a piping 9.
In the conventional rotary compressor, the injection opening 8 is closed by only a side surface of the rolling piston 4 fitted to the crank shaft 3. Accordingly, it is unavoidable that the wall thickness of the rolling piston 4 should be large in consideration of the inner diameter of the injection opening 8. This results in reduction in the inner diameter of the rolling piston 4 from the viewpoint of limitation of the inner diameter of the cylinder 1 thereby causing a small diameter of the eccentric part 2. When the diameter of the eccentric part 2 is small, reliability of the crank shaft is decreased and application to a compressor having a large capacity has been hindered.